HMT is bound at a special position in multiple occupied states in DR6 derivative crystals. (a, b) Stereo representations of the anomalous difference Fourier map (calculated with phases from the final DR6 model and anomalous differences from the W peak data set; contoured at 5σ) together with a ball-and-stick representation of the HMT cluster (large spheres represent the W atoms). The two symmetry-related HA cluster molecules are shown in dark grey and light grey. (a) A view along the crystallographic twofold symmetry axis (marked in red) and (b) a view perpendicular to it. (c) Two symmetry-related DR6 molecules are shown as a surface representation (coloured according to their calculated electrostatic potential) together with the bound HMT cluster molecules (yellow). Light and dark colours distinguish between the symmetry-related DR6 protomers. The location of the twofold symmetry axis is indicated in red.